UNIVERSITY OF CALIFORNIA
COLLEGE OF AGRICULTURE
AGRICULTURAL EXPERIMENT STATION
BERKELEY, CALIFORNIA
EXPERIMENTS WITH THE
TRANSPLANT ONION CROP
IN CALIFORNIA
GLEN N. DAVIS and H. A. JONES
BULLETIN 682
January, 1944
UNIVERSITY OF CALIFORNIA
BERKELEY, CALIFORNIA
CONTENTS
PAGE
Review of literature 3
Spacing tests 4
Time-of -transplanting studies 6
Size-of -seedling studies 10
Pruning studies 13
Time-of -harvest studies 15
Summary 19
Literature cited 20
1
EXPERIMENTS WITH THE TRANSPLANT ONION
CROP IN CALIFORNIA1
GLEN N. DAVIS2 and H. A. JONES8
The transplant onion crop of California consists chiefly of the early and the
so-called "intermediate" varieties. The early crop includes mainly Crystal
Wax, Early Grano, Crystal Grano, and San Joaquin. These are grown pri-
marily in the upper San Joaquin, Coachella, and Imperial valleys and in small
scattered acreages elsewhere in the state. The intermediate crop is grown
chiefly in the lower Sacramento and San Joaquin valleys and to some extent
along the coast, south of San Francisco. The varieties are chiefly Stockton
Yellow Globe, Red 21, Stockton G36, and Italian Red. Sweet Spanish, a late-
maturing onion, is also used to some extent for the transplant crop, especially
in Riverside, Los Angeles, and Kern counties. The transplant crop comprises
approximately one half of the total annual onion acreage in the state.
The culture is somewhat similar for the different varieties and for the dif-
ferent districts in the state. The seed of practically the entire transplant crop
is sown in open beds in the field, usually in late August or September (accord-
ing to the variety and the district) . The seedlings are taken to the field during
late fall or winter. Although there is a general conformity to certain practices,
there is little specific information about desirable practices in spacing, time of
transplanting, size of seedling used, and pruning (see figs. 1-4) . Data reviewed
or reported herein from California and several other states have thrown con-
siderable light on some of these problems.
REVIEW OF LITERATURE
In the lower Rio Grande Valley of Texas, Hawthorn (1)* secured heavier
yields for four consecutive years from the closer spacing when he compared
rows 14 and 16 inches apart, while spacing the plants uniformly in the row.
In Montana, Starring (5) compared Sweet Spanish transplants set 3 and 6
inches apart in the row. Although the weight per bulb was heavier for the
6-inch spacing, the heavier per-acre yields were secured for the 3-inch spacing.
In Utah, Wilson (6) seeded Sweet Spanish onions directly in the field and
then thinned to get the desired spacing of 2 to 10 inches between plants. With
each increase in distance between plants came a corresponding increase in the
percentage of doubles, and simultaneously a decrease in yield. Thinning
beyond 4 inches reduced not only the yield, but also the percentage of large
bulbs. In spacing tests with California Early Red in California, Jones {2)
found that with each increase in spacing of 3 to 12 inches came a delay in time
of maturity, an increase in the size of bulbs, and a decrease in the yield per
acre.
1 Received for publication March 26, 1943.
2 Assistant Professor of Truck Crops and Assistant Olericulturist in the Experiment
Station.
3 Principal Olericulturist, Division of Fruit and Vegetable Crops and Diseases, Bureau of
Plant Industry, Soils and Agricultural Engineering, Agricultural Eesearch Administration,
U. S. Department of Agriculture.
4 Italic numbers in parentheses refer to literature cited at the end of this publication.
[3]
4 University of California — Experiment Station
The results of priming reported by Hawthorn (i) for Yellow Bermuda
were somewhat inconsistent from year to year. For a five-year average, how-
ever, the unpruned plants gave the highest yield, and those with both tops
and roots pruned gave the lowest. Plants with only tops or roots pruned were
intermediate in yield. Kraus (3), working in Wyoming with the Early Grano
variety, compared unpruned transplants with those having about half the
foliage removed. He found no significant difference between pruned and un-
pruned plants in the total number of individuals that survived, or in the mean
weight per bulb, or in the number of marketable bulbs produced.
Hawthorn (1), comparing different-sized transplants of Yellow Bermuda,
found that those of medium size, weighing 5 to 7 grams and having a neck
TABLE 1
Weight of Onion Bulbs Grown at Different Spacings in the Row
Year
1927
1928
1929
1930
1931
1935
1935
1935
1942
1942
Location
Davis
Davis
Davis
Davis
Davis
Liberty Island
Liberty Island
Liberty Island
Shafter
Davis
Variety
California Early Red 21-6 .
California Early Red 21-24
California Early Red 21-6 .
California Early Red 21-24
Red 21
Early Grano
Stockton G36
Red 21
San Joaquin
Crystal Grano
Mean weight of bulbs (pounds) at the
given spacings (inches")
0 24
0.36
0.26
0.12
0.32
0.39
.41
.65
.41
.45
.36
.47
.38
.17
0.36
0.48
.51
.79
.55
.52
.38
.50
.45
.19
0.44
0.62
.66
.99
.83
.71
.44
.60
.50
.22
0.49
0.72
0.84
1.16
0.96
0.84
0.46
0.60
0.54
12
0.78
0.99
1.28
0.96
Difference
required for
signifi-
cance*
0.07
.08
.10
.08
10
05
08
05
05
0 06
* Difference required for significance at the 5 per cent point.
diameter of 6 to 9 millimeters, produced more U.S. No. 1 onion bulbs than
either larger or smaller transplants. If the transplants are very large, a high
percentage may form splits, doubles, and seedstems. Jones (2), in California,
found that large transplants of California Early Ked produced a higher yield
of bulbs and that the average size of the bulbs was larger.
SPACING TESTS
Methods. — Spacing tests were conducted at Davis from 1927 to 1931 with
different lines of California Early Red. Distances between plants in the row
were 3, 4, 6, 8, and 12 inches except in 1930, when the 12-inch spacing was
omitted. The rows were 18 inches apart. In 1927, they were 48 feet long; in
1 928, 36 feet ; in 1929, 1930, and 1931, 27 feet. Five replicates were planted in
1927, 1929, and 1930; three in 1928 and 1931.
In 1935 the spacing tests were located on Liberty Island near Rio Vista,
( 'alifornia. The varieties used were Red 21, Stockton G36, and Early Grano.
The plants were spaced 2, 3, 4, 6, and 8 inches in the row. The rows were 15
inches apart and 27 feel long. Four replicates were planted, and each spacing
was flanked by guard rows of the same spacing.
In 1942, spacing tests were located at Shafter and Davis. The variety San
Joaqnin was planted a1 Shafter; Crystal Grano at Davis. Plants were spaced
Bul. 682]
Experiments with the Transplant Onion Crop
2, 3, 4, and 6 inches apart in the row. The rows were 18 inches apart, 27 feet
long. Each spacing was replicated five times.
All data treated statistically were reduced by analysis of variance.
Results. — The data for 1927 to 1929, though presented earlier by Jones {2) ,
are included here as parts of tables 1 and 2 to bring together the work on
spacing. Results for the first three years showed definitely that the closest
spacing matured earliest, and as the spacing increased the plants matured
later. Apparently, therefore, environmental factors in addition to photoperiod
and temperature may influence the time of maturity. Data on time of maturity
were not collected after 1929.
TABLE 2
Yield of Onions Grown at Different Spacings in the Row
Year
Location
Variety
Yield (100-pound bags per acre) at
the given spacings (inches)
Difference
required for
signifi-
cance*
2
3
4
6
8
12
218
280
380
278
1927
California Early Red 21-6
California Early Red 21-24 ....
California Early Red 21-6
California Early Red 21-24 ....
Red 21
195
676
526
175
374
456
429
738
528
515
246
588
502
162
346
409
416
686
485
447
176
488
448
138
299
358
376
573
465
404
172
394
332
107
213
309
357
529
449
366
102
286
256
45
1928
48
1929
102
1930
— t
1931
51
1935
Liberty Island ....
Liberty Island ....
Liberty Island ....
Shafter
78
1935
Stockton G36. ..
82
1935
1942
Red 21
33
41
1942
162
* Difference required for significance at the 5 per cent point.
t No significant difference.
Every increase in spacing except one was accompanied by an increase in
average weight of bulb (table 1) ; but these increases were not always statis-
tically significant. The 3-inch spacing seemed to produce bulbs of the best size.
The necks were small, and they cured more readily than plants grown at the
wider spacing.
Yields per acre were always highest at the 2- and 3-inch spacings. A decrease
in yield per acre accompanied each increase in spacing except for Early Grano
at the 3-inch spacing. The low yields for Early Grano in 1935 were caused by
the high percentage of bolters (table 3). The extremely low yield for San
Joaquin at Shafter in 1942 resulted from a rather unfavorable growing season
and from lack of sufficient labor to complete the essential cultural operations.
However, results from spacing are directly comparable to other plots and in
no case did the increase in size of bulb at the wider spacings compensate for
the decrease in the number of bulbs harvested.
On Liberty Island in 1935, spacing at different distances produced no signi-
ficant differences in the percentage of bolters within varieties (table 3) . As is
well known, the size of plant is important in determining the percentage of
bolters ; but in these studies the increase in size of plant at the wider spacings
no doubt occurred too late in the season to be influenced by the environmental
conditions that influence bolting. Although the onion varieties differed con-
siderably in yield, they could not be compared statistically because they had
6 University of California — Experiment Station
been planted separately in several parts of the field. Stockton G36 produced
more seeders than Red 21 even though, in nearly all other plantings where
these two varieties could be compared, the latter produced the highest percent-
age of bolters.
TIME-OP-TRANSPLANTING STUDIES
Methods. — These studies were conducted at Davis from 1927 to 1934. From
1927 to 1930, different lines of California Early Red were used, whereas in
1931-32, Red 21, Stockton Yellow Globe, and a line of Italian Red were
TABLE 3
Percentage of Bolters at Different Spacings, at Liberty Island, 1935*
Spacing, inches
Early Grano
Stockton G36
Red 21
2
59.7
49.0
53.8
39.4
58.0
3.98
6.47
2.24
2.62
3.38
1.00
3
1 62
4
0 00
6
0.92
8
1 81
* No significant difference appeared in percentage of bolters (within varieties) at
different spacings.
planted. In 1927 the plots were planted in duplicate; in other years, in tripli-
cate. Single-row plots were used. Seeding was done at the usual time in late
August or early September ; transplanting, at different times in the late fall
and winter. Though only one seeding was made, there were six to eight trans-
planting dates. The 1933-34 experiments were handled somewhat differently.
Early, intermediate, and late varieties were included. Most of them were from
TABLE 4
Effect of Time of Transplanting on Mean Weight per Bulb and Yield per Acre in
California Early Red 21-6, at Davis, 1927
Date transplanted
Mean weight of
trimmed seed-
lings, grams
Bulbs
harvested
per plot
Mean weight
per bulb,
pounds
Yield per acre
(100-pound
bags)
January 18.
January 25.
February 1 .
February 18
February 22
March 1 . . . .
1.56
1.10
1.26
2.18
2.11
1.58
138
128
144
136
136
136
0 58
.50
.50
.41*
.36*
0 35*
489
389
436
336t
293*
283*
* Highly significant differences when compared with the January 18 planting.
t A significant difference when compared with the January 18 planting.
seed provided for a study of varietal types (4), and the strains are desig-
nated by the numbers originally assigned by the United States Department of
Agriculture. Two seedings were made of this material, an early and a late. The
early one came on September 6, 1933; the late one on November 6. The early-
^"'<lr<l plants were transplanted on December 8; the late-seeded on February
17. The transplants sot early were planted in duplicate plots, and those set late
in single plots.
Bul. 6S21
Experiments with the Transplant Onion Crop
Results. — The chief objectives in the time-of-transplanting tests were to
determine how the transplanting date affects the time of maturity, size of bulb,
yield per acre, and percentage of bolters.
The 1927 data (table 4) reveal no significant differences in the weight of the
trimmed seedlings for the different transplanting dates, nor in the number of
TABLE 5
Effect of Time of Transplanting on Mean Weight per Bulb and Yield per Acre in
California Early Bed 21-29, at Davis, 1928
Date transplanted
Mean weight of
trimmed seed-
lings, grams
Bulbs
harvested
per plot
Mean weight
per bulb,
pounds
Yield per acre
(100-pound
bags)
January 13
January 20
January 27
February 6
February 10
February 17
Difference required for significance
1.92
1.49
1.81
2.01
1.80
1.81
104
105
106
105
105
101
0.40
.39
.40
.35
.37
0.30
337
328
341
295
318
249
No significant
difference
No significant
difference
0.03
* Difference required for significance at the 5 per cent point.
bulbs harvested per plot. Except in the February 1 planting there was a
gradual decrease in weight of bulb, as well as in yield per acre, as the planting
date was delayed. There were no significant differences in weight of bulb nor
in yield per acre from the first three transplanting dates ; but seedlings set on
and after February 18 produced significantly smaller bulbs and lower yields
than those set January 18 or earlier.
TABLE 6
Effect of Time of Transplanting on Mean Weight per Bulb and Yield per Acre in
California Early Bed, at Davis, 1929
Date transplanted
Mean weight of
trimmed seed-
lings, grams
Bulbs
harvested
per plot
Mean weight
per bulb,
pounds
Yield per acre
(100-pound
bags)
January 9
January 16
January 23
January 30
February 6
February 13
February 20
February 27
Difference required for significance
0.82
.81
.82
.81
.60
.59
.58
0.57
701
689
449
457
465
459
0.17
3.4
0.08
* Difference required for significance at the 5 per cent point.
In 1928 the first transplanting was made on January 13, and successive
transplantings were made about once a week until February 17 (table 5). No
significant difference occurred in the weight of trimmed seedlings or in the
number of bulbs harvested per plot. Whereas the differences in mean weight
of bulbs harvested from the first three plantings were not significant, the last
8
University of California — Experiment Station
three plantings produced bulbs of significantly less weight than those from
the first planting. In yield per acre only the fourth and sixth plantings were
significantly lower than the first. In both 1927 and 1928 the last transplanting
produced the lowest yield. (See fig. 1.)
In 1929, weekty transplanting^ were made from January 9 to February 27
(table 6) — a total of eight. From January 16 on there was a gradual increase
in weight of transplant at each planting date, indicating that the weather
favored plant development during most of the winter. No significant differ-
ences occurred in the number of bulbs harvested per plot among the first four
planting dates ; after January 30, however, there was a considerable reduction
in the number of plants that survived. Very little difference in weight of bulb
TABLE 7
Effect of Time of Transplanting on Mean Weight per Bulb and Yield per Acre in
California Early Eed 21-24, at Davis, 1929-30
Date transplanted
Mean weight of
trimmed seed-
lings, grams
Bulbs
harvested
per plot
Mean weight
per bulb,
pounds
Yield per acre
(100-pound
bags)
December 24
3 34
2.61*
3.00*
3.94
5.46
5.60
70
80
77
c0
78
0 58
.53
.50
.52
53
0 30
488
458
418
434
February 18
451
301
Difference required for significance!
0.29
1.6
0.05
22
* Reduction in seedling weight due to error in sampling,
t Difference required for significance at the 5 per cent point.
occurred between the first four planting dates, nor between the last four plant-
ing dates. There was, however, considerable difference between the two groups
of planting dates. This same relation holds true for yield per acre.
In the winter of 1929-30, transplantings were made at approximately
2-week intervals from December 24 to March 7 (table 7). The weight of
trimmed seedlings planted after January 10 increased gradually. There was,
however, very little difference in the number of plants surviving, although
some of the differences were statistically significant. The mean weight of bulb
from the different planting dates was variable; but the largest bulbs were
secured from the first planting, and the smallest bulbs from the last one. The
first planting, made on December 24, produced bulbs approximately twice as
heavy as the last planting (made on March 7). In yield per acre the first
planting was significantly higher than any of the others, and the last planting
was the lowest.
In 1931-32, three varieties were planted at fairly regular intervals from
December 12 to March 7. The weight of bulb and the yield per acre decreased
with each delay in planting date, except for the January 18 planting (table 8) .
All varieties responded about the same to the delay in planting. For the Stock-
ton Yellow Olobe, Italian Red, and Red 21 the weight of the bulb of the
Doc-ember 12 planting exceeded that of March 7 by 158, 181, and 175 per cent,
rospootively, and llio yield per acre by 158, 189, and 167 per cent.
Bul. 682]
Experiments with the Transplant Onion Crop
These studies show that early planting produces the heaviest yields ; as the
transplanting date is delayed the yields are, in general, reduced. The seed-
lings usually make little growth aboveground during the winter in central
California, whether in the seedbed or in the field. Though climatic conditions
may not be suitable for foliage development, they usually do favor root
development. Plants set early develop an extensive root system during the
winter. When, accordingly, growth conditions become favorable, plants with
the most extensive root system develop most rapidly. Onion plants start to
bulb under temperature and photoperiodic conditions specific for the variety.
As a rule, when environmental conditions become favorable for bulbing, the
TABLE 8
Effect of Time of Transplanting on Mean Weight per Bulb and Yield per Acre in
Three Varieties of Onions, at Davis, 1931-32
Stockton Yellow
Globe 36-34
Italian Red
13-20-3
Red 21
Date transplanted
Mean
weight
per bulb,
pounds
Yield per
acre
(100-pound
bags)
Mean
weight
per bulb,
pounds
Yield per
acre
(100-pound
bags)
Mean
weight
per bulb,
pounds
Yield per
acre
(100-pound
bags)
0.98
.79
.64
.71
.60
51
0.38
767
609
504
545
448
369
297
0.73
.59
.52
.56
.47
.32
0.26
561
423
366
380
360
229
194
0 77
.68
.56
.56
.52
.38
0.28
631
568
January 4
445
482
443
February 15
320
March 7
236
Difference required for significance*
0 10
87
0 06
64
0 13
74
* Difference required for significance at the 5 per cent point.
larger plant will produce the larger bulb. Conditions that foster a large plant
also help, accordingly, to increase the bulb size and consequently the yield
per acre.
In 1933-34 numerous varieties were included, chiefly to determine the effect
of planting date on the percentage of bolters. Table 9 is arranged in the order
of decreasing percentage of bolters. The Spanish types seem to have a greater
tendency to bolt than others, White Sweet Spanish being highest with 71 per
cent. The two strains of Sweet Spanish showed a significant difference in the
percentage of bolters. Crystal Wax, Red Wethersfield, and Yellow Bermuda
also bolted rather badly in the early planting, whereas the Italian Red under
the same conditions, produced no bolters. Although these varieties may not
always be arranged in exactly the same order from year to year, the general
sequence should be similar. The same variety may vary considerably in per-
centage of bolters from year to year because of environmental conditions.
After a cool fall and a warm spring there is very little bolting. After a warm
fall and a cool spring the percentage of bolting is high. A warm fall favors
large plants, and this size accompanied by a cool spring provides the proper
complex for bolting.
(In every comparison in 1933-34 between the early and late planting of the
10
University of California — Experiment Station
same variety, the late planting produced a smaller bulb and fewer bolters. The
Spanish types produced a few bolters even in the late planting.
Judging from the data, the bolting habit is not correlated with pungency ;
varieties showing the most and also the fewest bolters are of the mild type.
SIZE-OF-SEEDLING STUDIES
Methods. — These studies were conducted at various times from 1927 to 1942.
Up to 1930 the tests were made at Davis with lines of California Early Red. In
1927 the plots were in duplicate; from 1928 to 1930, in triplicate. Single-row
TABLE 9
Influence of Different Seeding and Transplanting Dates on Weight of Bulb and
Percentage of Bolters in Different Varieties of Onions, at Davis, 1933-34
Variety
Strain
Weight of bulb, pounds
Early
planting*
Late
planting!
Bolters, per cent
Early
planting*
Late
planting t
White Sweet Spanish
Sweet Spanish
Sweet Spanish
Prizetaker
Crystal Wax
Red Wethersfield
Yellow Bermuda
Ailsa Craig
Early Yellow Globe
Southport Yellow Globe
Yellow Strassburg
Yellow Globe Dan vers. .
Mountain Dan vers
Mountain Dan vers
Southport White Globe.
Southport Red Globe. . .
Southport Red Globe. . .
Ohio Yellow Globe
Ebenezer
Australian Brown
Australian Brown t
Red 21
Italian Red
1
4
5
3
1
3
1
1
3
1
5
2
3
3
2
3
3
6
2
U.F.S.
13-20-3
0.57
.66
.72
.62
.30
.35
.31
.52
.45
.36
34
.34
.38
.40
.35
.30
.30
.32
.32
.30
.22
.44
0.48
0.31
0,44
0 41
0 40
0 13
0.16
0 11
0.34
0.17
0.16
0.12
71.1
68.8
20.8
67.9
54.0
44.2
40.9
37.3
35.4
35.4
30.0
24.1
21.8
23.9
22.5
16.8
22.0
18.8
18.9
9.8
7 4
1.8
0.0
2.6
3.8
0 0
0 0
0 0
0 0
0 0
* Seeded September 6, 1933, transplanted December 8, 1933.
t Seeded November 6, 1933, transplanted February 17, 1934.
t Late planting seeded October 25, 1933, transplanted February 24, 1934.
plots, 18 inches apart, were used. The transplants were set 4 inches apart in
the row. In 1935 the seedlings were started at Davis and transplanted to Lib-
erty Island near Rio Vista. The variety was Babosa. Seed was sown August 31,
and the seedlings were transplanted December 24. For transplanting, the
seedlings were grouped into eight size grades according to the diameter at the
lower sheath region. Some had started to bulb, a fact that accounts for the
large-diameter classes (table 11). The smallest size class — below % inch — and
the Largest — % to 1 inch — contained only sufficient plants for single plots; so
the data for these two sizes were not included in the analyses. For all other
sizes, dupl icate plots were planted. In 1936 two size classes of transplants were
compared at Milpitas, California, the varieties used being Stockton G36 (with
Bul. 682]
Experiments with the Transplant Onion Crop
11
the plots in triplicate), Stockton Yellow Globe (in quintuplicate), and Babosa
(in duplicate).
In 1942, Babosa was planted at Davis. Seedlings were separated into six
sizes according to the diameter at the lower sheath region. The largest size
class — over % inch — included enough plants for only two replications. As a
result, this size is not included in the analysis. All other sizes were replicated
five times.
Results. — From 1927 to 1930, lines of California Early Red were used to
determine how the size of the transplant affects the mean weight per bulb and
the yield per acre. The mean weight of the large seedlings was about twice that
of the small (table 10) at transplanting time. There was little difference in the
TABLE 10
Effect of Large and Small Onion Transplants on Stand, Mean Weight per Bulb, and
Yield per Acre, at Davis, 1927 to 1930
Year
Variety-
Size of
seedling
Weight
of trimmed
seedling,
grams
Bulbs
harvested
per plot
Weight
per bulb,
pounds
Yield
per acre
(100-pound
bags)
1927
Red 21
f Small
\ Large
J Small
1 Large
j Small
1 Large
f Small
\ Large
1.08
2.19*
1.06
2.56*
1.86
3.88*
2.60
5.38*
133
139
103
106t
76
76
78
79f
0.39
.51*
.32
.42*
.62
.77*
.42
0.56*
312
1928
1929
1930
California Early Red 21-9 . . .
California Early Red
California Early Red 21-24 . .
430*
262
361*
507
635*
354
479*
* Difference is highly significant.
f Difference is significant.
number of bulbs harvested per plot. Any differences that occur, however,
favored the larger seedlings. There was a very marked difference in yield per
acre and mean weight per bulb between small and large seedlings. For the
four-year period 1927 to 1930, the bulbs from large seedlings were 31, 31, 24,
and 33 per cent heavier, respectively, than those from the small seedlings. For
the same years the yield per acre from the large seedlings was 38, 38, 25, and
26 per cent higher than that from the small. According to these data, it would
seem advisable to adjust the seeding to prevent crowding in the bed or to dis-
card the small seedlings at transplanting time. Small seedlings may be the
result of crowding in the bed, but some of these may be caused by selfing in
the seed fields. As a rule, cross-pollination prevails in the onion seed fields ; but
there is considerable selfing when insects carry pollen from flower to flower of
the same plant. This self-pollination lessens vigor and therefore results in
smaller seedlings. As a result, bulbs are smaller and yields lower.
In 1935, seedlings of the variety Babosa of the same age, but of different
size, were planted on Liberty Island near Kio Vista, California. The trans-
plants were grouped into eight size grades according to the diameter at the
lower sheath region. Tte seedlings of this variety made a very rapid early
growth, and some bulbing occurred during the fall, a fact that accounts for
the large size classes. No bolters developed in the size class under % inch in
diameter, and only 1.4 per cent of the plants bolted in the Vs-to-1^ inch size
12
University of California — Experiment Station
(table 11). All classes over this size bolted badly, the percentage increasing
with the size of seedling.
In 1936 two size classes of seedlings of Stockton G36, Stockton Yellow
Globe, and Babosa were compared at Milpitas, California. The large-size trans-
plants of all three varieties produced the heaviest bulbs, but only in Stockton
Yellow Globe was the difference statistically significant (table 12). The yield
TABLE 11
Influence of Seedling Size on Percentage or Bolters in the Babosa
Variety of Onion, at Liberty Island, 1935
Seedling diameter,
inches
Bolters,
per cent
Seedling diamter,
inches
Bolters,
per cent
0 0
1.4
36 0
73 4
l-o-^-g
85 2
Ys-li
%-%...
R8 4
\i-y%
%-%
97 2
ys-li
y%-\
100 0
of Stockton G36 was practically the same from large and small seedlings.
Although the bulbs from the large transplants were larger, the yield was low
because of the numerous bolters. In Babosa the large seedlings yielded less per
acre than the small, because of bolters. Stockton G36, as might be expected,
bolted least ; it had been selected primarily for its delayed bolting habit.
Babosa produced the highest percentage of bolters, while Stockton Yellow
Globe took an intermediate position.
TABLE 12
Effect of Seedling Size on Number of Bolters, Weight of Bulb, and Yield per
Acre, at Milpitas, 1936
Variety
Seedling
diameter,
inches
Bolters
Bulbs
harvested
per plot
Weight
per bulls,
pounds
Yield
per acre
(] 00-pound
bags)
Stockton G36
ys-y4
H-H
ys-H
y*-%
2 3
11 0
21 1
21 1
28.5
50.5
78
69
50
57
49
2S
0 47
.54
.46
.R6*
.52
0 58
397
Stockton Yellow Globe
401
292
407
271
173
* Difference is highly significant.
Tn 1942, Babosa seedlings of the same age, separated into six size classes.
were compared at Davis (table 13). Since there were only enough plants for
two replications of 1hc over-%-inch class, these data were not included in the
analysis. As the size of transplant increased, the size of bnlb produced by
harvesl time increased in all except the ^-to-%-inch class. The differences
between succeeding classes were, however, not always significant. According
r<> the data for yield per acre, the larger seedlings produced the heaviest yield
except in the hist two classes, ;is given in the table. The reduction in yield here
no doubt results from the large number of bolters in these two classes. The
increase in size of hull) did not compensate for the reduction in the number of
Bul. 682]
Experiments with the Transplant Onion Crop
13
bulbs harvested. Where the seedlings planted were under % inch in diameter
the classes showed no significant differences in the percentage of bolters. Bolt-
ing was significantly more common in the classes over % inch than in those
below that size. Except in the %-inch-or-less class there was no significant dif-
ference in the number of bulbs harvested per plot. Many seedlings under %
inch in diameter failed to survive transplanting operations.
PRUNING STUDIES
Methods. — Pruning experiments were conducted in 1930, 1931, 1934, and
1942. In 1930 the variety used was California Early Red 21-24; in 1931,
Stockton Yellow Globe ; in 1934, Red 21 ; and in 1942, San Joaquin and Crystal
Grano. Four different pruning treatments were given : unpruned, roots
TABLE 13
Effect of Seedling Size, in the Variety Babosa, on Percentage of
Bolters, Mean Weight per Bulb, and Yield per Acre,
at Davis, 1942
Diameter of seedling,
inches
Bulbs
harvested
per plot
Bolters,
per cent
Mean
weight
per bulb,
pounds
Yield
per acre
a00-pound
bags)
38
54
62
66
55
38
0 0
0 0
2.6
4 4
22 4
16 0
0.18
.23
.58
.79
.74
0.83
76.3
Yr^i
137.3
M-%
397 0
H-H
565.2
444.1
311.0
Difference required for significance. . .
14t
19*
11. 6t
16 Oi
0 12f
0.16|
41. 9t
57. 8t
* Did not enter into the analysis.
t Difference required for significance at the 5 per cent point.
% Difference required for significance at the 1 per cent point.
pruned, tops pruned, roots and tops pruned. In 1930, 1931, and 1942 the tops
were trimmed 5 inches above the stem plate ; in 1934, 6 inches above it. Roots
were trimmed to a length of 1 inch. This method of trimming both roots and
tops conforms closely with commercial practice. All plants were set in shallow
furrows made with a hand plow so that the long roots of the unpruned plants
could be covered. Transplants were set 4 inches apart in rows 18 inches apart
and 27 feet long. In 1930 there were seven replicates ; in 1931, three ; in 1934,
fourteen ; and in 1942, five. In 1930 the seedlings were transplanted on Febru-
ary 8 ; in 1931, on February 3 ; the 1934 crop, on November 21, 1933; and the
1942 tests, on December 19, 1941.
Results. — The pruning of onion seedlings to facilitate transplanting is a
common practice. To what extent it influences yield has not been definitely
determined. According to the results of other investigators, pruning is of no
benefit except in making transplanting easier. At Davis, California, in 1930,
the unpruned seedlings of California Early Red 21-24 produced a larger bulb
and a greater yield per acre than any of the pruning treatments (table 14).
Cutting back both roots and tops of an individual plant reduced the weight of
14
University of California — Experiment Station
the mature bulb. Pruning either the roots or the tops gave the plant a less
severe check than pruning them both. Root pruning seemed to produce the
least injury.
In 1931 (table 15) the differences in weight of bulb between the various
treatments were not significant. The treatments arranged themselves, how-
TABLE 14
Effect of Pruning Onion Transplants on Stand, Mean Weight per
Bulb, and Yield per Acre, in thei Variety California
Early Red 21-24, at Davis, 1930
Treatment
Unpruned
Roots pruned
Tops pruned
Roots and top3 pruned
Difference required for significance
Bulbs
harvested
per plot
78
No significant
difference
Mean weight
per bulb,
pounds
0.69
0.62
0.62
0.57
0.03*
0.06f
Yield per acre
(100-pound
bags)
589
534
527
47S
33*
45f
* Difference required for significance at the 5 per cent point,
f Difference required for significance at the 1 per cent point.
ever, in about the same order (relative to bulb size) as in 1930. Unpruned^
seedlings and those with only the roots pruned produced the heaviest bulbs. In
yield per acre the transplants with both tops and roots trimmed yielded sig-
nificantly less than the unpruned or those with only the roots pruned.
In 1934 the unpruned lots were significantly heavier, in both weight per
TABLE 15
Effect of Pruning Onion Transplants on Stand, Mean Weight per
Bulb, and Yield per Acre, in the Variety Stockton
Yellow Globe, at Davis, 1931
Treatment
Bulbs
harvested
per plot
Mean weight
per bulb,
pounds
Yield per acre
(100-pound
bags)
78
SO
78
78
0.51
0 50
0 49
0 44
427
428
412
Roots and tops pruned
367
Difference required for significance. . .
No significant
difference
No significant
difference
, nfi*
* Difference required for significance at the 5 per cent point.
bulb and yield per acre, than those of other treatments; and, as before, the
seedlings with both tops and roots pruned made the poorest showing (table 16).
In 1942 pruning studies were made at Davis with two varieties, San Joaquin
and Crystal Grano (table 17). For San Joaquin there was no significant dif-
ference in the mean weight of bulbs from the different treatments nor in the
yield per acre, though there was a significant difference in the number of bulbs
harvested ]>er plot. With Crystal Grano tliere was no significant difference
Bul. 682] Experiments with the Transplant Onion Crop
15
between the number harvested nor the mean weight. The yield per acre from
transplants with both tops and roots pruned was significantly lower, however,
than the yield from any other treatment.
TIME-OF-HARVEST STUDIES
Methods. — To determine how time of harvest affects yield, two blocks were
selected in a field of California Early Red onions at Davis. Block 1 was divided
TABLE 16
Effect of Pruning Onion Transplants on Stand, Mean Weight per
Bulb, and Yield per Acre, in the Variety Eed 21, at Davis, 1933-34
Treatment
Bulbs
harvested
per plot
Mean weight
per bulb,
pounds
Yield per acre
(100-pound
bags)
71
67
G7
67
0 48
0 44
0 44
0 43
361
314
314
307
Difference required for significance . .
No significant
difference
0 02*
0 03t
31*
41*
Difference required for significance at the 5 per cent point.
i required for significance at the 1 per
f Difference requi
cent point,
into three sub-blocks, each having nine rows or plots. The first harvest was
made on June 3, and succeeding harvests came at intervals of 4 or 5 days
until July 12. Immediately after each harvest the plants were dried in shallow
trays. Weighing was done 10 days after harvest. Block 2 was divided into five
sub-blocks, each having six rows or plots of onions. The first harvest was made
on June 17, and the last on July 12.
TABLE 17
Effect of Pruning Onion Transplants on Stand, Mean Weight per Bulb, and Yield
per Acre, in the Varieties San Joaquin and Crystal Grano, at Davis, 1942
Treatment
San Joaquin
Bulbs
harvested
per plot
Mean
weight
per bulb,
pounds
Yield
per acre
(100-pound
bags)
Crystal Grano
Bulbs
harvested
per plot
Mean
weight
per bulb,
pounds
Yield
per acre
(100-pound
bags)
Unpruned
Roots pruned
Tops pruned
Roots and tops pruned
0.47
0 45
0 48
0 48
320
273
273
262
0.34
0.34
0.35
0.31
147
151
127
105
Results. — The object of the time-of -harvest experiments was to determine
about how much the yield was reduced when the plants were pulled at differ-
ent times before maturity. As is shown by data from block 1 (table 18), there
was a gradual increase in weight of bulb from June 3 to July 12, and a con-
siderable increase in yield per acre even after most of the tops were down. The
weight of the bulb was affected somewhat by the climatic conditions during
16
University of California — Experiment Station
TABLE 18
Effect of Harvest Date on Mean Weight per Bulb and Yield per
Acre in California Early Eed Onions, Block 1, at Davis, 1927
Date harvested
Bulbs
harvested
per plot
Tops down,
per cent
Mean
weight
per bulb,
pounds
— ■ 1
Yield
per acre
(100-pound
bags)
133
133
133
130
133
125
130
131
136
12.3
26.5
45 6
76.9
87.3
94.6
100.0
100.0
100.0
0 37
.42
.42
.47
.48
.45
.51
.51
0.52
296
June 8
335
343
June 17
354
June 22
388
June 27
342
July 2
401
July 7
404
July 12
430
Difference required for significance. . .
No signifi-
cant
difference
9.3*
12. 8f
0.04*
0.06t
34*
47t
* Difference required for significance at the 5 per cent point.
t Difference required for significance at the 1 per cent point.
TABLE 19
Effect of Harvest Date on Mean Weight per Bulb and Yield per
Acre in California Eary Red Onions, Block 2, at Davis, 1927
Date harvested
Bulbs
harvested
per plot
Tops down
per cent
Mean
weight
per bulb,
pounds
Yield
per acre
(100-pound
bags)
June 17
June 22
June 27
July 2
July 7
July 12
134
127
131
140
137
140
28.0
36.1
78.1
79.3
94 9
92.8
0 33
.35
.38
.38
39
0.39
270
268
303
325
324
335
Difference required for significance .
No signifi-
cant
difference
8.2*
11. 2f
No signifi-
cant
difference
No signifi-
cant
difference
* Difference required for significance at the 5 per cent point.
t Difference required for significance at the 1 per cent point.
the 10-day curing period before weighing;. Lots exposed to strong desiccating
winds lost more weight than lots not so exposed. Probably a better method
would have been to remove the tops and roots and weigh the bulb at time of
harvest.
The data from block 2 (table 19) show the same trend. There was, however,
no significant difference between harvest dates in mean weight of bulb or in
yield per acre.
Bul. 682] Experiments with the Transplant Onion Crop 17
Fig. 1. — Plants transplanted to the field at different dates ; dug and photographed
on March 2, 1928, to show the extent of root and top development. From left to right,
these groups of plants were set out, respectively, January 13, 20, and 27 and Febru-
ary 6, 10, and 17, 1928.
Fig. 2. — Stockton Yellow Globe seedlings for transplanting, grown on raised beds
in peat land in the Delta region of California. Seed was drilled thickly in rows 3 to 4
inches apart. (From Cir. 357.)
18
University of California — Experiment Station
Fig. 3. — California Early Red and Stockton Yellow Globe seedlings
for transplanting; grown in raised beds (two rows to the bed) near
Sacramento.
I i
%**$
Hl
■:■ A
- .
IP
v^^f^c^w
.;0-
J
%£':*l"n:.r. ::::;>: ;<»-,
"-Mi
■? % :
" , : /'
.■:■/''."
V
Slip::,. ■ :,
■; ■ ■ ■ . ■
■ ■ ■■■"■■■-"-■ :'";■■■ ;:", ■■■■'.
Y\g. 4. — California Early Red seedlings for transplanting; grown on
raised beds (four rows to the bed) near Sacramento. The seedlings in
the two outside rows of each bed were the largest and were pulled first.
Bul. 682] Experiments with the Transplant Onion Crop 19
SUMMARY
In spacing tests during seven years, as the spacing distance between plants
in the row was increased beyond 2 or 3 inches there was an increase in the size
of bulb and a decrease in yield per acre. For the varieties tested, the 3-inch
spacing appeared best. The plants matured well, and there was no crowding
in the row. The different spacing had no influence on the percentage of bolters
for the one year (1935) in which records were taken.
Time-of -transplanting studies throughout six years show definitely that
early planting produces larger bulbs and heavier yields per acre. Plants set
early form a vigorous root system during the winter and therefore develop
more rapidly with the advent of warm weather. Early transplanting of bolting-
varieties, however, greatly increases the percentage of bolters.
In every comparison between large and small transplants made at Davis
during five years, the differences in favor of large transplants for size of bulb
were either significant or highly significant, and the differences in yield per
acre were all highly significant. In a one-year test at Milpitas the large seed-
lings produced the largest bulbs ; but not all differences were significant, and
no significant differences occurred in yield per acre.
A gradual increase in the percentage of bolters (0 to 100 per cent) occurred
in the variety Babosa as the size of transplant was increased from under %
inch to % or 1 incn in diameter.
In pruning tests for four years, a considerable reduction in yield often
occurred when transplants had both roots and tops trimmed, as is usually
done in commercial practice. In two of the four years the differences in yield
between unpruned transplants and those with roots pruned, tops pruned, or
both roots and tops pruned were highly significant. In two of the years there
was very little difference between the unpruned transplants and those with
either tops or roots pruned. In all four years, except with the variety San
Joaquin grown at Shaf ter in 1942, the difference between the unpruned trans-
plants and those with both tops and roots pruned was either significant or
highly significant.
According to time-of -harvest studies, onions continue to increase in size
and in yield per acre for some time after most of the tops break over.
20 University of California — Experiment Station
LITERATURE CITED
1. Hawthorn, L. R.
1938. Cultural experiments with Yellow Bermuda onions under irrigation. Texas Agr.
Exp. Sta. Bui. 561:1-30.
2. Jones, H. A.
1929. Spacing, time of planting, and size of seedling studies with California Early Bed
onions. Amer. Soc. Hort. Sci. Proc. 26:114-18.
3. Kraus, J. E.
1942. Effects of partial defoliation at transplanting time on subsequent growth and
yield of lettuce, cauliflower, celery, peppers, and onions. U. S. Dept. Agr. Tech.
Bui. 829:1-35.
4. Magruder, Roy, et ah
1041. Description of types of principal American varieties of onions. U. S. Dept. Agr.
Misc. Pub. 435:1-85.
5. Starring, C. C.
1935. Comparison of some methods of growing onions. Montana Agr. Exp. Sta. Bui.
305:1-11.
6. Wilson, A. L.
1934. Influence of spacing on the formation of "double onions." Utah Acad. Sci. Arts
and Letters 11:177-84.
12m-2, '44(8277)
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